Minimum Volume Standards: An Incentive To Perform More Radical Cystectomies?

Take Home Message Minimum volume standards for radical cystectomy do not seem to create an unwanted incentive to perform more surgeries.


Introduction
Minimum volume standards (MVS) for hospitals and surgeons have been a subject of discussion since 1979, when Luft et al [1] hypothesized that there is a relationship between higher surgical volume and lower postoperative mortality. The idea behind this relationship is the ''practice makes perfect'' principle, whereby patients in high-volume hospitals (HVHs) would benefit from a higher degree of surgical experience than patients in low-volume hospitals (LVHs). Surgical experience applies not only to the surgical team performing the procedure but also to the ward staff, facilities, and infrastructure involved in postoperative care [2,3].
This volume-outcome relationship has been extensively studied across multiple surgical fields [4][5][6]. In 2002, Birkmeyer et al [4] investigated 14 types of cardiovascular and cancer surgeries in a cohort of 2.5 million procedures and found lower mortality for higher hospital volume for all 14 procedure types. Similarly, multiple systematic reviews found lower mortality or complication rates in hospitals with higher volume for different types of surgery [7][8][9][10][11].
Regarding oncological urology, several studies have shown a clear volume-outcome relationship for radical cystectomy (RC) and the European Association of Urology (EAU) recommends that hospitals perform at least ten and preferably more than 20 RCs annually [2,12]. In the past 20 yr, multiple countries have introduced MVS for different types of surgical procedures, including RC [13]. In the Netherlands, an MVS of 10 RCs for bladder cancer per hospital per year, using 3-yr averages, was introduced by the Dutch Urology Association in 2010. In 2015 this MVS was raised to 20 RCs annually per hospital.
MVS and their effects on the centralization of health care remain controversial. MVS opponents emphasize their possible negative consequences. For instance, centralization leads to fewer training opportunities for junior staff. Patients and family members could experience a greater travel burden not only for the procedure itself but also for preoperative and postoperative appointments. For patients in rural areas, this can ultimately lead to reduced access to care. Finally, MVS implementation can result in an unwanted incentive to perform surgery. For example, lowgrade and/or low-stage bladder cancer normally does not require radical surgical treatment, but urologists might still be inclined to perform RC in such patients to meet the MVS [14][15][16][17]. In a qualitative interview study from 2018, Dutch surgeons reported that this undesired strategic behavior sometimes occurs [14]. Similarly, Hlatky [15], Schwartz et al [16], and Stanak and Strohmaier [7] all debated the possibility of this ''perverse incentive'' as a result of MVS implementation. The objective for the current study was to examine whether MVS lead to an unwanted incentive to perform more RCs. To this end, we analyzed data from all hospitals that performed RCs in the Netherlands between 2006 and 2017. We hypothesized that if an MVS results in an unwanted incentive for hospitals to perform more RCs, an increase in the number of RCs outside the recommended indication (cT2-4a N0 M0 and high-risk nonmuscle-invasive bladder cancer), such as for non-high-risk stage cT1 and/or advanced stage cT4 Nx Mx disease, might be observed, which we later refer to as a stage-shift hypothesis. In addition, an increase in the number of RCs performed in the final quarter of the year (later referred to as an end-ofyear-sprint hypothesis) might be observed. These effects might be expected in hospitals for which the annual number of RCs did not meet but approximated the MVS and in the first 3 yr after MVS implementation, since MVS adherence is determined using 3-yr averages.

2.1.
Cohort and data

Statistical analysis
Descriptive statistics were calculated to describe the IVH and HVH

Patient characteristics
In total, 9608 patients with bladder cancer who underwent RC in the Netherlands between 2006 and 2017 were selected from the NCR. The RCs were performed in 95 different hospitals. Table 1 presents the patient and tumor characteristics for those treated with RC in the IVH and HVH settings during period 1 (n = 1410). Among these patients, 15% had non-muscle-invasive bladder cancer (NMIBC), 52% had cT2 stage muscle-invasive bladder cancer (MIBC), and 28% had cT3+ stage MIBC. There was no difference in sex distribution between the groups, while the median age was 68 yr in the IVH cohort and 67 yr in the HVH cohort (p = 0.003). More patients received neoadjuvant treatment (radiotherapy, chemotherapy, or both) in the HVH setting than in the IVH setting (17% vs 8%; p < 0.001). Table 2 lists the patient and tumor characteristics for those treated with RC in the IVH and HVH settings in period 2 (n = 1356) are presented. Among these patients, 18% had NMIBC, 46% had cT2 stage MIBC, and 32% had cT3+ stage MIBC. During period 2, the sex distribution was similar between the two settings; the median age was 70 yr in the IVH cohort and 68 yr in the HVH cohort (p < 0.001). Some 20% of patients treated in HVHs received neoadjuvant treatment versus 16% of patients in IVHs (p = 0.2).

3.2.
Stage-shift hypothesis  Regarding the second MVS, Figure 2 shows the proportion of T1 and T4b cases in the RC cohort for IVHs (6 hospitals) and HVHs (10 hospitals) in period 2. The reference period for the second MVS was 2011-2013. The distribution of other disease stages for the RC cohort during this period is shown in Supplementary Figure 2. During the reference period, 13% of tumors treated with RC in IVHs were stage

Discussion
In this nationwide cohort study we did not find any convincing evidence that MVS gave an unwanted incentive to perform more RCs in patients with bladder cancer in the Netherlands. Notably, this was also not found in hospitals that approximated the MVS, during the first years after its implementation. There were no indications of a shift in disease stage or of an increase in RCs in the final quarter of the year after MVS implementation. The proportion of RCs for cT1 and advanced disease stages remained stable after implementation of the MVS. In the Netherlands, RC is indicated in patients with cT2-4a N0/Nx M0 disease, in accordance to the EAU guidelines for MIBC [20]. For cT1 tumors, in contrast to some other countries, RC is only indicated in bacillus Calmette-Guérin-unresponsive patients and is generally not performed for treatment-naïve highgrade cT1 tumors. Therefore, a sudden increase in the num-  ber of RCs for cT1 tumors after implementation of a new MVS could have been an indication of an MVS-induced incentive to perform more RC procedures. In addition, there was no increase in the proportion of patients with cT1 or advanced-stage bladder cancer treated with RC in IVHs compared to HVHs. In fact, HVHs had a slightly higher proportion of cT4/N+/M+ tumors treated with RC in all periods evaluated. Similar results were observed in a Dutch study on hospital volume for esophageal resections: Wouters et al [21] found that stage IV dis-ease accounted for 17% of resections in HVHs versus 6% in LVHs. This could be explained by the fact that HVHs are often large hospitals with more expertise in this specific type of surgery. Patients with advanced disease stages are more likely to be referred to more experienced hospitals and those hospitals might be more inclined to perform surgery on advanced tumors. Furthermore, our results do not support the end-of-year-sprint hypothesis. All RCs were divided equally among the four quarters and there was no evidence of an increase in the number of RCs in the final To the best of our knowledge, this is the first nationwide study to examine whether MVS implementation represents an unwanted incentive to perform more surgeries in addition to the intended effect of centralization. Data for all hospitals that performed RCs between 2006 and 2017, as well as all tumor and patient data for the RCs, were available through the NCR, so our study results represent the effect of MVS implementation on a nationwide basis. Lastly, implementation of two different MVS in the Netherlands was included. This provides insights into the effects of nationwide introduction of a new volume standard, as well as the consequences of setting an even stricter MVS.
The findings from our study should be viewed in light of some limitations. First, the IVH cohort in period 2 (2015-2017) included only six hospitals and 314 patients. Because of these small numbers, we cannot draw strong conclusions from the data. In addition, we aggregated the data on stage distribution for the first 3 yr after MVS implementation, as the numbers were too small to investigate on a year-toyear basis.
Second, we categorized hospitals as IVHs and HVHs using volume as a dichotomous variable. If possible, the use of nonlinear splines to build a model with volume as a continuous variable is preferred over dichotomization. However, building a sufficiently flexible model given the relatively low number of hospitals included in the current study is potentially problematic. Hence, we opted for a simpler modeling strategy. Future studies in other countries that include more hospitals should consider use of more flexible modeling strategies with volume as a continuous variable. Third, up to 2012, only RCs that were part of the initial treatment for the first noninvasive or first (muscle-) invasive bladder cancer were recorded in the NCR. Therefore, the number of RCs performed for MIBC after an earlier diagnosis of T1 disease before 2012 will be slightly higher than reported. We do not expect this to have affected our results, since our study focused specifically on a stage shift in RCs for cT1 and/or cT4b bladder cancer. Fourth, we did not investigate the effect of MVS on oncological outcomes. However, this was previously studied by Richters et al [22], who found that 30-d and 90-d mortality slightly increased with hospital volumes up to 25   this information is not available through the NCR because of privacy legislation. Notwithstanding its limitations, the current study contributes useful results to the ongoing debate regarding MVS criteria. While there is convincing evidence of positive effects on the mortality and morbidity associated with complex surgery [4][5][6], there are opponents of centralization who emphasize the possible negative effects of MVS. These include greater travel times, reduced access to care, limitations on teaching opportunities for junior staff, and the possibility of an unwanted incentive to perform more surgeries [14,15,[23][24][25]. Some studies have addressed these problems. For instance, Hentschker and Mennicken [26] reported that centralization of care in Germany for patients with an abdominal aortic aneurysm or hip fracture improved outcomes without compromising overall access to care with regard to travel time. In any case, for a relatively small country such as the Netherlands, travel time is not expected to be a major limiting factor for centralization. A study by Xia et al [27] on associations between travel distance, hospital volume, and outcomes for patients undergoing RC concluded that the benefits of undergoing RC at a HVH outweigh the potential disadvantages of a longer travel distance. However, studies addressing the possibility of an MVS-induced unwanted incentive to perform more surgeries were lacking, which was the motivation for the present work.

Conclusions
In conclusion, we found no evidence of an unwanted incentive to increase the indication for radical surgery because of MSV introduction for RC. This result adds to the growing body of literature that favors MVS implementation. Other: None.
Financial disclosures: J. Alfred Witjes certifies that all conflicts of interest, including specific financial interests and relationships and affiliations relevant to the subject matter or materials discussed in the manuscript (eg, employment/affiliation, grants or funding, consultancies, honoraria, stock ownership or options, expert testimony, royalties, or patents filed, received, or pending), are the following: None.
Funding/Support and role of the sponsor: None.